图片服务 API

astro:assets 旨在让任何图片优化服务都能轻松地在 Astro 之上构建服务。

¥astro:assets was designed to make it easy for any image optimization service to build a service on top of Astro.

什么是图片服务？

¥What is an Image Service?

Astro 提供两种类型的图片服务：本地和外部。

¥Astro provides two types of image services: Local and External.

本地服务在静态站点构建时直接处理图片转换，或在开发模式和按需渲染的运行时处理图片转换。这些通常是 Sharp、ImageMagick 或 Squoosh 等库的封装。在开发模式和按需渲染的生产路由中，本地服务使用 API 端点进行转换。
外部服务指向 URL，可以添加对 Cloudinary、Vercel 或任何符合 RIAPI 的服务器等服务的支持。

使用图片服务 API 进行构建

¥Building using the Image Services API

服务定义采用具有各种所需方法 (“hooks”) 的导出默认对象的形式。

¥Service definitions take the shape of an exported default object with various required methods (“hooks”).

外部服务提供指向输出 <img> 标记的 src 的 getURL()。

¥External services provide a getURL() that points to the src of the output <img> tag.

本地服务提供 transform() 方法来对图片执行转换，以及 getURL() 和 parseURL() 方法，用于在开发模式和按需渲染时使用端点。

¥Local services provide a transform() method to perform transformations on your image, and getURL() and parseURL() methods to use an endpoint for dev mode and when rendered on demand.

两种类型的服务都可以提供 getHTMLAttributes() 来确定输出 <img> 和 validateOptions() 的其他属性，以验证和增强传递的选项。

¥Both types of services can provide getHTMLAttributes() to determine the other attributes of the output <img> and validateOptions() to validate and augment the passed options.

外部服务

¥External Services

外部服务指向要用作最终 <img> 标记的 src 属性的远程 URL。该远程 URL 负责下载、转换和返回图片。

¥An external service points to a remote URL to be used as the src attribute of the final <img> tag. This remote URL is responsible for downloading, transforming, and returning the image.

import type { ExternalImageService, ImageTransform, AstroConfig } from "astro";

const service: ExternalImageService = {
  validateOptions(options: ImageTransform, imageConfig: AstroConfig['image']) {
    const serviceConfig = imageConfig.service.config;

    // Enforce the user set max width.
    if (options.width > serviceConfig.maxWidth) {
      console.warn(`Image width ${options.width} exceeds max width ${serviceConfig.maxWidth}. Falling back to max width.`);
      options.width = serviceConfig.maxWidth;
    }

    return options;
  },
  getURL(options, imageConfig) {
    return `https://mysupercdn.com/${options.src}?q=${options.quality}&w=${options.width}&h=${options.height}`;
  },
  getHTMLAttributes(options, imageConfig) {
    const { src, format, quality, ...attributes } = options;
    return {
      ...attributes,
      loading: options.loading ?? 'lazy',
      decoding: options.decoding ?? 'async',
    };
  }
};


export default service;

本地服务

¥Local Services

要创建你自己的本地服务，你可以指向内置端点 (/_image)，也可以另外创建你自己的可以调用服务方法的端点。

¥To create your own local service, you can point to the built-in endpoint (/_image), or you can additionally create your own endpoint that can call the service’s methods.

import type { LocalImageService, AstroConfig } from "astro";

const service: LocalImageService = {
  getURL(options: ImageTransform, imageConfig: AstroConfig['image']) {
    const searchParams = new URLSearchParams();
    searchParams.append('href', typeof options.src === "string" ? options.src : options.src.src);
    options.width && searchParams.append('w', options.width.toString());
    options.height && searchParams.append('h', options.height.toString());
    options.quality && searchParams.append('q', options.quality.toString());
    options.format && searchParams.append('f', options.format);
    return `/my_custom_endpoint_that_transforms_images?${searchParams}`;
    // Or use the built-in endpoint, which will call your parseURL and transform functions:
    // return `/_image?${searchParams}`;
  },
  parseURL(url: URL, imageConfig) {
    return {
      src: params.get('href')!,
      width: params.has('w') ? parseInt(params.get('w')!) : undefined,
      height: params.has('h') ? parseInt(params.get('h')!) : undefined,
      format: params.get('f'),
      quality: params.get('q'),
    };
  },
  transform(buffer: Uint8Array, options: { src: string, [key: string]: any }, imageConfig): { data: Uint8Array, format: OutputFormat } {
    const { buffer } = mySuperLibraryThatEncodesImages(options);
    return {
      data: buffer,
      format: options.format,
    };
  },
  getHTMLAttributes(options, imageConfig) {
    let targetWidth = options.width;
    let targetHeight = options.height;
    if (typeof options.src === "object") {
      const aspectRatio = options.src.width / options.src.height;

      if (targetHeight && !targetWidth) {
        targetWidth = Math.round(targetHeight * aspectRatio);
      } else if (targetWidth && !targetHeight) {
        targetHeight = Math.round(targetWidth / aspectRatio);
      }
    }

    const { src, width, height, format, quality, ...attributes } = options;

    return {
      ...attributes,
      width: targetWidth,
      height: targetHeight,
      loading: attributes.loading ?? 'lazy',
      decoding: attributes.decoding ?? 'async',
    };
  },
  propertiesToHash: ['src', 'width', 'height', 'format', 'quality'],
};
export default service;

在静态站点和预渲染路由的构建时，<Image /> 和 getImage(options) 都会调用 transform() 函数。它们分别通过组件属性或 options 参数传递选项。转换后的图片将构建到 dist/_astro 文件夹中。它们的文件名将包含传递给 propertiesToHash 的属性的哈希值。此属性是可选的，默认为 ['src', 'width', 'height', 'format', 'quality']。如果你的自定义图片服务有更多更改生成图片的选项，请将这些选项添加到数组中。

¥At build time for static sites and pre-rendered routes, both <Image /> and getImage(options) call the transform() function. They pass options either through component attributes or an options argument, respectively. The transformed images will be built to a dist/_astro folder. Their file names will contain a hash of the properties passed to propertiesToHash. This property is optional and will default to ['src', 'width', 'height', 'format', 'quality']. If your custom image service has more options that change the generated images, add these to the array.

在开发模式下，当使用适配器按需渲染时，Astro 无法提前知道哪些图片需要优化。Astro 使用 GET 端点（默认为 /_image）在运行时处理图片。<Image /> 和 getImage() 将其选项传递给 getURL()，后者将返回端点 URL。然后，端点调用 parseURL() 并将结果属性传递给 transform()。

¥In dev mode and when using an adapter to render on demand, Astro doesn’t know ahead of time which images need to be optimized. Astro uses a GET endpoint (by default, /_image) to process the images at runtime. <Image /> and getImage() pass their options to getURL(), which will return the endpoint URL. Then, the endpoint calls parseURL() and passes the resulting properties to transform().

获取配置图片服务和图片配置

¥getConfiguredImageService & imageConfig

如果你将自己的端点实现为 Astro 端点，则可以使用 getConfiguredImageService 和 imageConfig 调用服务的 parseURL 和 transform 方法并提供图片配置。

¥If you implement your own endpoint as an Astro endpoint, you can use getConfiguredImageService and imageConfig to call your service’s parseURL and transform methods and provide the image config.

要访问图片服务配置（image.service.config），你可以使用 imageConfig.service.config。

¥To access the image service config (image.service.config), you can use imageConfig.service.config.

import type { APIRoute } from "astro";
import { getConfiguredImageService, imageConfig } from 'astro:assets';

export const GET: APIRoute = async ({ request }) => {
  const imageService = await getConfiguredImageService();

  const imageTransform = imageService.parseURL(new URL(request.url), imageConfig);
  // ... fetch the image from imageTransform.src and store it in inputBuffer
  const { data, format } = await imageService.transform(inputBuffer, imageTransform, imageConfig);
  return new Response(data, {
      status: 200,
      headers: {
        'Content-Type': mime.getType(format) || ''
      }
    }
  );
}

查看内置端点为完整示例。

¥See the built-in endpoint for a full example.

钩子

¥Hooks

`getURL()`

本地和外部服务所需

¥Required for local and external services

getURL(options: ImageTransform, imageConfig: AstroConfig['image']): string

对于本地服务，此钩子返回生成图片的端点的 URL（用于按需渲染和开发模式）。在构建期间不使用它。getURL() 指向的本地端点可以同时调用 parseURL() 和 transform()。

¥For local services, this hook returns the URL of the endpoint that generates your image (for on-demand rendering and in dev mode). It is unused during build. The local endpoint that getURL() points to may call both parseURL() and transform().

对于外部服务，此钩子返回图片的最终 URL。

¥For external services, this hook returns the final URL of the image.

对于这两种类型的服务，options 是用户作为 <Image /> 组件的属性或作为 getImage() 的选项传递的属性。它们属于以下类型：

¥For both types of services, options are the properties passed by the user as attributes of the <Image /> component or as options to getImage(). They are of the following type:

export type ImageTransform = {
    // ESM imported images | remote/public image paths
    src: ImageMetadata | string;
    width?: number;
    height?: number;
    widths?: number[] | undefined;
    densities?: (number | `${number}x`)[] | undefined;
    quality?: ImageQuality;
    format?: OutputFormat;
    alt?: string;
    [key: string]: any;
};

`parseURL()`

本地服务所需；不适用于外部服务

¥Required for local services; unavailable for external services

parseURL(url: URL, imageConfig: AstroConfig['image']): { src: string, [key: string]: any}

此钩子将 getURL() 生成的 URL 解析回具有不同属性的对象，以供 transform 使用（用于按需渲染和开发模式）。在构建期间不使用它。

¥This hook parses the generated URLs by getURL() back into an object with the different properties to be used by transform (for on-demand rendering and in dev mode). It is unused during build.

`transform()`

仅本地服务所需；不适用于外部服务

¥Required for local services only; unavailable for external services

transform(buffer: Uint8Array, options: { src: string, [key: string]: any }, imageConfig: AstroConfig['image']): { data: Uint8Array, format: OutputFormat }

该钩子转换并返回图片，并在构建过程中被调用以创建最终的资源文件。

¥This hook transforms and returns the image and is called during the build to create the final asset files.

你必须返回 format 以确保为用户提供正确的 MIME 类型以进行按需渲染和开发模式。

¥You must return a format to ensure that the proper MIME type is served to users for on-demand rendering and development mode.

`getHTMLAttributes()`

本地和外部服务可选

¥Optional for both local and external services

getHTMLAttributes(options: ImageTransform, imageConfig: AstroConfig['image']): Record<string, any>

该钩子根据用户传递的参数 (options) 返回用于将图片渲染为 HTML 的所有附加属性。

¥This hook returns all additional attributes used to render the image as HTML, based on the parameters passed by the user (options).

`getSrcSet()`

Added in: astro@3.3.0

对于本地和外部服务都是可选的。

¥Optional for both local and external services.

getSrcSet?: (options: ImageTransform, imageConfig: AstroConfig['image']): SrcSetValue[] | Promise<SrcSetValue[]>;

该钩子生成指定图片的多个变体，例如，在 <img> 或 <picture> 的 source 上生成 srcset 属性。

¥This hook generates multiple variants of the specified image, for example, to generate a srcset attribute on an <img> or <picture>’s source.

该钩子返回具有以下属性的对象数组：

¥This hook returns an array of objects with the following properties:

export type SrcSetValue = {
  transform: ImageTransform;
  descriptor?: string;
  attributes?: Record<string, any>;
};

`validateOptions()`

本地和外部服务可选

¥Optional for both local and external services

validateOptions(options: ImageTransform, imageConfig: AstroConfig['image']): ImageTransform

该钩子允许你验证和增强用户传递的选项。这对于设置默认选项或告诉用户需要参数非常有用。

¥This hook allows you to validate and augment the options passed by the user. This is useful for setting default options, or telling the user that a parameter is required.

查看 validateOptions() 如何在 Astro 内置服务中使用。

¥See how validateOptions() is used in Astro built-in services.

用户配置

¥User configuration

配置要在 astro.config.mjs 中使用的图片服务。配置采用以下形式：

¥Configure the image service to use in astro.config.mjs. The config takes the following form:

import { defineConfig } from "astro/config";

export default defineConfig({
  image: {
    service: {
      entrypoint: "your-entrypoint", // 'astro/assets/services/sharp' | string,
      config: {
        // ... service-specific config. Optional.
      }
    }
  },
});